A typical cellular network may include one or more radio access networks (RANs), each of which may be arranged to provide mobile stations with access to one or more transport networks such as the public switched telephone network (PSTN) and/or the Internet. The RAN may include, for example, a cellular base station (e.g., base transceiver station, access node, eNodeB, or the like), which may include an antenna configuration and associated equipment for radiating to define one or more coverage areas in which a mobile station can wirelessly communicate with the base station over an air interface. The base station may operate according to a defined air-interface protocol such as CDMA, LTE, WiMAX, and/or GSM, and the mobile station may operate according to the same air-interface protocol to enable and facilitate communicating with the base station and gaining access to one or more transport networks via the RAN.
One or more carrier frequencies (“carriers”) form the physical transmission interface of an air-interface link between a mobile station and a RAN. Each carrier typically takes the form of a pair of radio frequencies. For example, radio waves of one frequency may be used to transmit forward-link data from the RANs to the mobile stations, while radio waves of another frequency may be used to transmit reverse-link data from the mobile stations to the RANs. Further, a RAN may communicate with multiple mobile devices on any given forward- or reverse-link carrier.
Logical channels of the physical transmission interface may be used to send and/or receive traffic, control, and broadcast data, as examples. Channels take different forms under different types of air-interface protocols. In TDMA (time division multiple access) networks, channels typically take the form of one or more timeslots of a repeating waveform on a carrier frequency used by multiple mobile stations. In other words, in TDMA networks, different mobile stations on different channels take turns using the full transmit power of the base station at different times. In CDMA (code division multiple access) networks by contrast, different mobile stations on different channels simultaneously share the transmit power of the base station. In such networks, different channels are delineated by the RAN applying different codes to different channels.
Base stations in a given RAN may be arranged to broadcast in each of their coverage areas a respective pilot signal (or reference signal), which may enable mobile stations to select an appropriate coverage area in which to operate. The mobile stations may correspondingly scan for these pilot signals and attempt to register in a coverage area that is broadcasting a sufficiently strong signal.
When a mobile station enters into coverage of the RAN, such as coverage of a base station, the mobile station may engage in a registration (e.g., attach) procedure. During this procedure, the mobile station may transmit a registration-request message via a reverse-link control channel (such as an access channel) to the base station providing the coverage area. Upon receiving that registration-request message, the base station may transmit to the mobile station via a forward-link control channel a registration-response message, acknowledging the registration.
After registering with a RAN, a mobile station may operate in an idle mode on a carrier frequency in a coverage area (e.g., a sector) provided by a base station of the RAN. If another network entity such as a telephone, computer, or other communication device attempts to contact the mobile station, then the RAN will typically send the mobile station a page message via a forward-link control channel. The mobile station may respond by requesting establishment of a communication session over a traffic channel and then conducting the relevant communication via the established communication session. In other instances, the mobile station may initiate contact with another network entity, in which case the mobile station sends the RAN an access-request message in order to request establishment of a communication session over a traffic channel and then conducts the relevant communication via the established communication session.